In many delayed coking processes heavy gas oil boiling in the range of about 625.degree. F. to about 900.degree. F. at atmospheric pressure is the heaviest liquid drawn off the coker fractionator. This material is usually subjected to treatment in fluid catalytic crackers for conversion to lighter products. However, due to the refractory nature of heavy gas oil, treatment of such material in such fluid catalytic crackers is often harmful to the catalysts used therein. The detrimental affect on the catalysts affects not only the heavy gas oil being treated in the fluid catalytic cracker, but also other refinery streams that may be co-fed to the cracker. The practice of cracking heavy gas oil in fluid catalytic crackers continues to be a significant practice in many refineries due to the lack of other reliable options available to such refineries. It would be advantageous if a process could be developed for upgrading heavy gas oil as well as similar hydrocarbonaceous materials without having to do so in a fluid catalytic cracker.
U.S. Pat. No. 2,271,097 discloses a process for converting high boiling hydrocarbons into lower boiling hydrocarbons. The process includes the step of heating the bottoms from a fractionator in a viscosity breaker at a temperature of 850.degree.-950.degree. F. and a pressure of 75-500 psig.
U.S. Pat. No. 3,172,840 discloses a process for converting hydrocarbonaceous materials such as petroleum oils to gasoline and middle distillates. The process includes the step of cracking a product stream boiling in the range of 750.degree.-950.degree. F. from a coker bubble tower in a thermal cracking furnace at a temperature of 850.degree.-1000.degree. F. and a pressure of 300-1000 psig.
U.S. Pat. No. 4,213,846 discloses a delayed coking process that employs a hydrotreating step wherein gas oil from the coker fractionator is hydrotreated at a temperature of 315.degree.-400.degree. C. (599.degree.-752.degree. F.) and a hydrogen partial pressure of 350-2000 psig.
U.S. Pat. No. 4,784,746 discloses a process for upgrading crude oil (whole crude or topped crude) by combining the crude oil with a low boiling component that boils below 330.degree. F. and has an aromatic content of at least 20%, then heating the resulting mixture at 400.degree.-500.degree. C. (752.degree.-932.degree. F.) and a pressure sufficient to maintain the feed stream in the liquid phase. The reference discloses pressures in the range of 100-1000 psig. The process is conducted for an effective period of time to increase the proportion of non-residual components in the crude oil using a transalkylation process.
U.S. Pat. No. 4,840,725 discloses a process for converting high boiling hydrocarbons to lower boiling materials characterized by an increase in aromatic content and a lower pour point which comprises contacting said high boiling hydrocarbons with water at a temperature of from about 600.degree. F. to about 875.degree. F. and a pressure of at least about 2000 psi in the absence of any externally supplied catalysts, and wherein the weight ratio of water to high boiling hydrocarbons is from about 0.5:1 to about 1:1, and the water and high boiling hydrocarbon form a substantially single phase system under the elevated temperature and pressure conditions used.